We propose to evaluate the hypothesis that endogenous opiates play a role in modulating female sexual functioning during coitus. Using animal subjects, we will determine the effects of naloxone, and opiate antagonist, on female sexual functioning and the extent to which naloxone can block or reverse the effects of stimuli associated with copulation. Other tests of this hypothesis will be conducted by determining: (1) if exogeneous opiate administration has the same effects on female sexual functioning as extensive sexual stimulation, and (2) if acute administration of opiates produces 'cross tolerance' to sexual stimulation.